The national monitoring program is financed by the Swedish Agency for Marine and Water Management. Monitoring is performed by the Swedish Museum of Natural History. Data are stored in the Swedish Ocean Archive (SHARK) by the Swedish Meteorological and Hydrological Institute (SMHI). Information about the program and the methods are available in Swedish at the website of Swedish Agency for Marine and Water Management, https://www.havochvatten.se/overvakning-och-uppfoljning/miljoovervakning/marin-miljoovervakning/tumlare.html

In relation to Danish MSFD monitoring the data maps microplastics content in sediments in Danish waters. Data covers 13 sediment samples from the Belt Sea and its fjords, Kattegat and Limfjord. The samples were taken in 2018-2021 and analyzed in 2020-2021. A study of variation of microplastics over short distances, consisting of 13 sediment samples taken in a grid in Odense Fjord in 2021. The survey showed that microplastic could be found in all sediment samples in concentrations ranging from 22 to 7402 µg kg-1 (microgram microplastic per kg sediment dry matter). As number of microplastic particles, this corresponded to between 508 and 23340 N kg-1 (number of microplastics per kg of sediment dry matter) Odense Fjord showed that the microplastic content at this locality varied greatly. The average mass concentration was 4683 µg kg-1 with a range from 250 to 24848 µg kg-1 . Measured as a number, the concentration averaged 18671 N kg-1 with a range from 7266 to 34141 N kg-1 .

In a pilot study, microlitter was sampled with a Ferry Box system on the commercial ferry (M/S Color Line Fantasy) between Oslo and Kiel. The system acquired samples in the Danish part of the Skagerrak and Kattegat. In total thirteen samples were collected from September 2019 to February 2020 using mesh sizes 100 and 500 µm. Eleven samples were successfully processed. The samples were subsequently processed and analysed for chemical composition using FTIR. Microplastic amounts found ranged from 0 to 1.85 fragments or fibers per m3 (average 0.71 per m3).

Microlitter was sampled with a module fitted on a Ferry Box system on the commercial ferry cruises (M/S Color Line Fantasy) between Oslo and Kiel. The system acquired samples in the Danish part of the Skagerrak and Kattegat. In total seven samples were collected from 23-10-2020 to 02-11-2020 using filters of mesh sizes of 300 and 500 µm. Particles were visually identified and analysed for chemical composition using FTIR. Particle concentrations ranged from 0.39 to 1.85 particles per m3 (average 0.91 per m3).

Contents and composition of microplastic-like particles have been analysed in ten sediment samples from the Danish part of the open North Sea and in the Inner Danish waters in 2015. The contents of microplastic-like particles in the size range 100-5000 µm were determined to be in the range of 192-3511 particles per kg dry weight sediment, dominated by blue and black coloured particles, mainly as fibres, and particle sizes < 300 µm were dominating.

This study is a first attempt in Denmark on assessing the presence of microplastics in our open & coastal waters from Baltic to North Sea. The occurrence and impact of microplastics have in the Danish initial assessment for EU’s Marine Strategy Framework Directive (MSFD) been identified as a relevant indicator for describing “Good Environmental Status” (GES) for descriptor 10 on Marine Litter. Microplastic particles in marine waters, which consist of synthetic polymer materials, origin mainly from secondary microplastics, i.e. fragments of litter like solid waste, fishing gear, paint flakes etc. from either sea- or land based sources. Primary microplastics (engineered) are not expected to be as common as secondary microplastics. Microplastics can origin from both local sources and from long-range transport with ocean or air currents.